Don't get me wrong, there was a lot of great lines in it and the Hitler red herring was fine but Mels is Melody will be River all wrapped up that quickly and cleanly? That doesn't give the character or story the treatment it deserves.
I thought it was enough, close to perfect.
There was a wonderful metaphor going on in the episode, which might have been obscured by Hitler in the cupboard, the robot full of miniaturized cross people, and the poisoned Fred Astaire routine: Amy and Rory are looking for their daughter. It turns out she was an important part of their lives from the very beginning, they just didn't realize it, it wasn't the way expected, and they come into this knowledge after it's too late to change any of it. They're stuck with the lives they've led, despite knowing a bloke with a time machine.
Except for knowing the bloke w/the time machine part, this is pretty much true of everyone's life. It's not what we expect, it's all we have, and, if we're lucky, we can look back with our memories and find the good and meaningful things we didn't know the significance of at the time.
I didn't need (any more of) the machinations of plot. We know how River dies, how she was born, that she was kinda-sorta raised by, or at least alongside of, her parents, we now know we've been watching the story not only two people falling in love, but how they redeemed each other. Anything more would be going through the motions.
There's also something lovely about the title; it's not just an attention-grabber and a red herring, it dovetails straight into the overarching theme. On the surface, it's the line that every SF fan has always wanted to hear in their favorite show or story (which had time travel). And, I'm sure, it's a line every Who writer has always wished they had the freedom to
write. It speaks to the power of the whole genre: we can do
anything, set any wrong to right, look at the endless redemptive power at our disposal!
Except what can you
never do in a time travel story? Kill Hitler. Or your grandparents. You should even be careful around butterflies in the Pleistocene. There are things we cannot undo without losing ourselves.
Maybe it's just me, but I love the way Mels could
say, "Let's kill Hitler", the way it could be given voice, but, in the end, not
done, because even with fantasy, with a time machine, there's a hard limit to what can be taken back. Sometimes redemption is reconciliation, it is letting go, making peace, falling in love with your assassin, giving your life for your victim, and realizing the only childhood you'll share with your daughter is the one you had...
I'll stop now

!
...is just a bit too far-fetched for my tastes.
I'll say this: Moffat combines sentimentality and gamesmanship into something I find irresistible. I want to believe!